• Arnd Bergmann's avatar
    tcp: use monotonic timestamps for PAWS · cca9bab1
    Arnd Bergmann authored
    Using get_seconds() for timestamps is deprecated since it can lead
    to overflows on 32-bit systems. While the interface generally doesn't
    overflow until year 2106, the specific implementation of the TCP PAWS
    algorithm breaks in 2038 when the intermediate signed 32-bit timestamps
    overflow.
    
    A related problem is that the local timestamps in CLOCK_REALTIME form
    lead to unexpected behavior when settimeofday is called to set the system
    clock backwards or forwards by more than 24 days.
    
    While the first problem could be solved by using an overflow-safe method
    of comparing the timestamps, a nicer solution is to use a monotonic
    clocksource with ktime_get_seconds() that simply doesn't overflow (at
    least not until 136 years after boot) and that doesn't change during
    settimeofday().
    
    To make 32-bit and 64-bit architectures behave the same way here, and
    also save a few bytes in the tcp_options_received structure, I'm changing
    the type to a 32-bit integer, which is now safe on all architectures.
    
    Finally, the ts_recent_stamp field also (confusingly) gets used to store
    a jiffies value in tcp_synq_overflow()/tcp_synq_no_recent_overflow().
    This is currently safe, but changing the type to 32-bit requires
    some small changes there to keep it working.
    Signed-off-by: default avatarArnd Bergmann <arnd@arndb.de>
    Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    cca9bab1
tcp_ipv4.c 67.6 KB